Burrowing owls have an affinity for
the dung of other animals. Their underground nests and surrounding areas
are carpeted with the stinky stuff. Now a team of researchers has found at
least one reason why all this fecal matter matters to the owls: It's bait
for dung beetles, the owls' favorite grub.

The research, reported in today's issue of the science journal
Nature, demonstrates that burrowing owls (Athene
cunicularia) deliberately use mammal dung as a tool to reel in a
meal—and in the process substantially increase the number of dung beetles
they eat.

"Burrowing owls are diurnal [active in daytime], they will sit at the
burrow entrance all day long and it looks like they're doing nothing,"
said Douglas Levey, a zoologist at the University of Florida in
Gainesville. "But you know what? It's pretty clear they are fishing.
They've got their line in the water and are waiting for dung beetles to
come by."

A burrowing owl stands
at the entrance to its burrow, surrounded by the animal dung that it has
positioned, perhaps to entice dung beetles. Researchers tested nest
burrows in Florida and found that if the dung was removed the owls
replaced it rapidly, suggesting that it is more than an incidental
accumulation of debris.

Levey, who is the lead author of the study, added that the finding is
particularly noteworthy because it demonstrates that tool use can
substantially benefit a wild animal. Such convincing evidence is scant in
the biological record.

For example, herons are widely known to place a floating object, such
as a bread crumb or feather, on top of water as a lure for minnows. But no
studies have compared how well herons would do if they did not fish in
this manner.

"As far as I know, [our study] is the first example of that, not just
in birds but in wild animals in general," Levey said.

Gavin Hunt, an ecologist at the University of Auckland in New Zealand
who studies tool use by crows, agrees.

"The owl paper is the first to really quantify the benefit of tool use
to a free-living animal in terms of food gained," he said. "As such, it is
an interesting finding that seems to confirm what most of us have only
assumed to date."

Experiment

The researchers came up with the study idea several years ago while on
a field trip to observe burrowing owls. It was part of an ornithology
course Levey was teaching at the University of the Florida.

Levey and his students—including study co-authors Scot Duncan, now at
Birmingham-Southern College in Alabama, and Carrie Levins, who lives in
Panama City, Florida—noticed dung scattered around the burrow and wondered
why it was there.

Duncan, whose wife happens to be a beetle expert, recognized beetle
parts in the regurgitated pellets that were mixed in with the dung. He
realized that the owls were eating a bunch of beetles.

"Everybody who studies burrowing owls knows they bring dung back to
their burrows, and they know that burrowing owls eat a lot of dung
beetles. But nobody had put two and two together," Levey said.

To test the hypothesis that the burrowing owls were indeed luring the
dung beetles to their nests with dung, the researchers removed dung and
pellets from several burrows. They then placed fresh dung at the entrance
to some and left others bare.

Four days later the researchers examined the owls' regurgitated pellets
and found that the owls with dung bait ate ten times more dung beetles and
six times more dung beetle species than the owls without dung bait.

Wise Owls?

But before you go out and buy your favorite burrowing owl a kitschy
"gone fishin'" sign to hang on the burrow wall, Levey said there is no
evidence to suggest the owls are actually aware of what they are doing.

"Even though people think owls are wise, there's no reason to assume
they make a conscious choice to go get the dung they bring back because
[they know] beetles will then appear out of nowhere," he said.

Rather, according to Levey, this dung beetle baiting behavior is likely
a trait that evolved via natural selection: Owls that bring back more dung
are more likely to get more dung beetles and thus are more likely to be
successful in reproduction, passing on the trait.

"The owls are using a rather simple method to catch beetles with
readily available material, so the raw material—owls, dung, and dung
beetles—if you like, was just waiting for evolution to come up with tool
use," Hunt, the New Zealand ecologist, said.

In fact, Levey doubts that the behavior of bringing dung back to the
burrow evolved for the reason of dung beetle baiting. Owls bring other
stuff back to the burrows, including bits of plastic, carpet tailings,
foil, and gum wrappers, all of which may serve as insulation. Or, the dung
may serve to camouflage from predators the scent of eggs or chicks.

The researchers tested the egg hypothesis using quail eggs and found
that nests with and without dung were equally attacked by predators.
However, the test did not rule out the possibility that chicks give off a
smell that the dung masks.

Regardless, the researchers' finding that the dung beetle baiting
behavior benefits the owls' diet is generally held to be valid.

"I'm convinced that owls with dung outside their burrows catch more
dung beetles than when the dung is not there," Hunt said. "That doesn't
rule out another advantage of having the dung around the burrows, though."

Levey said, "It's often the case that one behavior can do more than one
thing, and there's nothing wrong with that."

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Soaring on specially adapted wings, they
silently stalk their prey under the cover of darkness, their
eyes and ears fixed on the catch. Some people find these
"ghost" owls ominous—spooky agents of death that haunt
abandoned buildings and litter their roosts with the crushed
bones of their unlucky victims.

It doesn't help that
these creatures, commonly known as barn owls, don't "hoot" but
emit raspy screeches and hissing noises.

Yet the barn
owl isn't all that scary. Contrary to its reputation among
some people, it does not eat larger animals such as chickens
and cats.

And far from being a nasty raptor, the barn
owl is ecologically important for natural rodent control.

"Barn owls perform a valuable service to agriculture.
They control rodent and other pest populations," said Richard
Raid, an owl researcher at the University of Florida's
Everglades Research and Education Center.

Barn owls
get their name from their tendency to nest in abandoned
buildings, especially barns in areas surrounded by lush
meadows, grasslands, marshes, and fields. The birds are also
known as "ghost" owls for the white face and underbelly
feathers that are visible as they fly overhead.

Studies in the United States, Britain, Canada, and
other countries have found substantial declines in barn owl
populations over the past half century. The main factor blamed
for the decline is the loss of farm land to rapid development,
which has wiped out the bird's favored nesting sites and
habitats.

As part of efforts to reverse the population
decline, many farmers, conservationists, and other citizens
are installing nesting boxes to lure barn owls and boost their
reproduction.

The New Caledonian crow is one of the few birds that
probes for food with twigs, a form of tool use. Now, three
Oxford University, England researchers have discovered that
one such crow, a captive female, has gone a step further.

To obtain out-of-reach food, the crow repeatedly took
a piece of straight wire and bent it to create a hook.
According to the researchers, who report their findings in the
August 9, 2002 issue of Science, this behavior suggests
that New Caledonian crows "rival nonhuman primates in
tool-related cognitive capabilities."

New Caledonian
crows living in the wild do create hooked probes from twigs,
but the captive crow did something very different.

"To
our knowledge, there are no confirmed reports of any animal
making a hook out of unnatural material, such as wire, to
solve a new problem," said Alex Kacelnik, a behavioral
ecologist who coauthored the report with Alex A. S. Weir and
Jackie Chappell.